The present invention relates to boilers and more particularly to methods of disrupting vapour films formed in film boiling in boilers and to boilers with means for disrupting such vapour films.
In conventional boilers, heat transfer rates across the interfaces between the fire space and the liquid space of the boiler can be limited by the phenomenon of film boiling. Film boiling is the forming of films of liquid vapour at the walls of the liquid space of the boiler. The presence of such vapour films significantly reduces the rates of heat transfer into the boiler liquid which can be maintained. In order to avoid film boiling, it has been necessary hitherto to allow for lower heat transfer rates per unit area across the interface between the fire space and the liquid space and to use, instead, relatively large areas of such interface to achieve desired total heat transfer rates. This results in boilers being relatively large, containing for instance, very great lengths and quantities of liquid tubes, to provide the necessary area of interface.